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Old 04-19-2013, 07:24 PM   #1066
Vulfy OP
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So basically my whole argument behind this, is that "slow" and "fast" are terms that need definition.

A bike might look almost stationary when its going around the cone, so it looks "slow", but if we look at just the front wheel, we see that it swings around the cones, quite "fast".


Duncan, am I even close to anything reasonable here, or just whistling out of my ass?
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Old 04-20-2013, 05:11 PM   #1067
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Today's session.




FUN!
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Old 04-20-2013, 08:28 PM   #1068
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Vulfy - Thanks again for setting everything up today and getting the video up so quickly.

Sent from my SAMSUNG-SGH-I727 using Tapatalk 2
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Old 04-20-2013, 08:58 PM   #1069
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"Ballast" wants to know where you get your funky music from. Thanks again for the new nickname for my fiance.

Some more pictures from today:







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Old 04-21-2013, 12:28 AM   #1070
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Hey Vulfy & co, I have not gone back to look but I think your all looking great out there, improving immensely. In the latest vid you all look very smooth & controlled. Impressed I am!

Shirley the "ballast" could not weigh more than a couple of bags of sugar? She could fit in the top box. I would be interested to read how it feels pillioning on a course. Not a lot of time to relax.
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Old 04-21-2013, 11:17 AM   #1071
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Quote:
Originally Posted by Harvey Krumpet View Post

Hey Vulfy & co, I have not gone back to look but I think your all looking great out there, improving immensely. In the latest vid you all look very smooth & controlled. Impressed I am!

Shirley the "ballast" could not weigh more than a couple of bags of sugar? She could fit in the top box. I would be interested to read how it feels pillioning on a course. Not a lot of time to relax.
Abby frowns upon the bags of sugar comment.

For the rest she says:

1. Get used to the feeling of falling over. It's probably not good for a new passenger.

2. She had to look over my shoulder in the direction of the turn. That small weight shift really helped the bike to turn.

3. Put more weight on your legs instead of sitting so that it's easier to keep your balance.
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Old 04-21-2013, 12:13 PM   #1072
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Heh, sorry about the the whole "ballast" thing

As far as the music, that was all by Ratatat.

Harvey, yeah we are having a blast doing this. These guys are picking it up really fast, I'm actually a little bit jealous. It took me months to wrap my head around navigating around the course smoothly.

I'll try to film a bit more next time, as I doubt I will have my rear rotor fixed for next weekend, to ride the course hard. Should be fun to capture the entire day, from setting up the course, to them practicing and warming up tires in figure 8, to tail chasing, and maybe even some timed attacks. Hopefully we will get a few more people next time as well. The more the merrier.

2-up riding was really impressive for me to watch.
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Old 04-22-2013, 03:44 AM   #1073
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Yesterday, In Amsterdam we had a ladies-only gymkhana experience
I think there were about 15 ladies with bikes.

To bad I wasn't there, but I understood that they had a great time.
Pictures are on it's way
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Old 04-22-2013, 08:04 AM   #1074
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Yeah! Pictures pictures pictures.
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Old 04-22-2013, 08:41 AM   #1075
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Quote:
Originally Posted by liquid_ice View Post
Yesterday, In Amsterdam we had a ladies-only gymkhana experience
I think there were about 15 ladies with bikes.

To bad I wasn't there, but I understood that they had a great time.
Pictures are on it's way
wow , cool !
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Old 04-22-2013, 08:58 AM   #1076
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Vulfy - Excellent explanation, but I'll take your word for the figures. I have the new VBOX Sport data logger so what I will do is get one of our better riders to do a couple of rotations, one with the logger GPS sensor mounted over the front wheel spindle and one with it mounted over the rear wheel spindle. Although the actual circles picked up by the data logger will be smaller than the circles described by the bike, due to the bank angle, I'm sure we can get some figures that are broadly correct.

Of course when we are looking at how fast the bike can be turned we always have to factor in the tyre slip angle which adds a layer of complication to the sums!
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Old 04-22-2013, 10:48 AM   #1077
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Quote:
Originally Posted by Motogymkhanaman View Post
I have the new VBOX Sport data logger so what I will do is get one of our better riders to do a couple of rotations, one with the logger GPS sensor mounted over the front wheel spindle and one with it mounted over the rear wheel spindle.
Is GPS precise enough to provide meaningful data? As I understand, GPS accuracy (without using WAAS) is on the order of a couple of meters. Since the front and rear wheel contact patch is roughly two meters apart on a typical motorcycle, I would think the margin of error is such that it would be hard to tell much difference in the radii of the circles traced by the front and rear tires. Nevertheless, it's all theory until you actually give it a try. I'll be interested in the results regardless :)
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Old 04-22-2013, 11:33 AM   #1078
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Couldn't you just lean the bike over with the steering locked and walk it in a circle with someone following behind putting marks on the ground
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Old 04-22-2013, 12:54 PM   #1079
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Please note that everything below is written with a U-turn or a full 360 turn in mind. Going into a shallower turn is a bit different. Here I'm talking about braking at the cone, and doing a U-turn around it.

At this point, its interesting to find out the actual speed difference between the wheels, front and rear.

Finding out just the turning radius of each wheel is easy enough. As you said you can just trace the wheels as you duck walk it around at full lock. Leaning the bike is a bit harder due to the weight, but can be done with a few people.

However, as I said, the interesting thing to see is the speed difference between wheels.

You can see how top riders turn around, their rear wheel is drawing an extremely tight circle around the cone, so it travels very little distance, in a turn.

However the front wheel has to keep up with the turn rate of the rear wheel, but at a larger radius arch, which will make it travel much faster compared to rear wheel.

What I'm fascinated about, is that the perceived "speed" of a motorcycle traveling through space vs turn rate around the cone.

If we look at the motorcycle as a whole, it looks to travel slowly around the cone. Simply because its rigidly connected to rear wheel, which travels short distance when turning around the cone. So the ENTIRE silhouette of the motorcycle looks to be moving slowly through space.

However the swing of the front wheel is much faster, and that is a speed of rotation, which is somewhat high, as it needs to keep in line with rear tire, but at a much wider arch.

I think the whole point of this thought exercise is for beginner riders to realize that going "slow" does not necessarily mean going slow.

Going slow in a straight line is not the same as going "slow" around the cone. The bike might look "slow" going around the cone, but throttle input, and the feeling ON the bike, is very different to going slow in a straight line.

I think for beginner riders, it is important to understand this distinction. I know I struggled a lot more trying to slow down the motorcycle too much around the corner.
I was fighting it against the gravity too much, when instead I should have probably relied more on momentum I was carrying, and concentrating more on the proper inputs through my body position and handlebars.

Basically all I'm trying to say is, don't go too slow into a turn, where you are struggling to keep the bike from falling over. You need a bit of momentum, you need RPMs to pick the bike up, you need brakes to balance out your power input, and you need to feel the bike, and let it do what it needs to do.

Bike needs to fall into the turn, but not fall because of lack of power, but because of momentum and the mass of the bike against the brakes. There is always a point in a turn, where you will feel the bars twisting from your hands, into the turn. That means that the transfer of weight under braking is twisting the front wheel into the turn, tightening the turn. If we don't fight it, do it smoothly and in control, the turn will naturally tighten, and at the scariest moment when we feel as if we are falling over, the bike WILL pick itself up and straighten out, usually already at the exit of the turn

But all of that will happen ONLY if you have enough power and momentum going into the turn, otherwise you will either flop on your side, or you will panic and straighten the bars out, and widen your turn considerably.

So yeah... don't go "slow".
At least that is my personal experience so far.
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Old 04-23-2013, 04:19 AM   #1080
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Excellent explanation there Vulfy. We have a saying that "If you try to go fast, you will end up going slow".

What we mean by this is that a lot of riders have only ever had experience of banking their bike whilst travelling at a reaonable speed and few, if any, have experience of the handlebars turning significantly whilst doing so. Because of this a lot of new riders try to maintain their balance by travelling at too high a speed as they turn around a pylon. This leads to the build up of a significant tyre slip angle and so they naturally make a very large arc around the pylon. Distance is the thief of time, so these big arc's all add up to the rider taking a much longer path around the pylons and obstacles than they need to.

Getting riders to believe that the bike will lean over quite happily at low speeds so long as it is changing direction quickly, is one of those key Moto Gymkhana riding skills that we need to encourage.
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